Botch Is a γ-Glutamyl Cyclotransferase that Deglycinates and Antagonizes Notch

Botch promotes embryonic neurogenesis by inhibiting the initial S1 furin-like cleavage step of Notch maturation. The biochemical process by which Botch inhibits Notch maturation is not known. Here, we show that Botch has gamma-glutamyl cyclotransferase ( GGCT) activity that deglycinates Notch, which prevents the S1 furin-like cleavage. Moreover, Notch is monoglycinated on the g-glutamyl carbon of glutamate 1,669. The deglycinase activity of Botch is required for inhibition of Notch signaling both in vitro and in vivo. When the gamma-glutamyl-glycine at position 1,669 of Notch is degylcinated, it is replaced by 5-oxy-proline. These results reveal that Botch regulates Notch signaling through deglycination and identify a posttranslational modification of Notch that plays an important role in neurogenesis.